This Program Project, Cellular and Molecular Biology of Lipoprotein Metabolism, is designed to explore the fundamental aspects of the interaction of plasma lipoproteins with mammalian cells and tissues. To this end, we have proposed four main areas of investigation, each of which is closely related to the others. The major theme or goal of this multidisciplinary collaborative project is to define those pertinent modifications of cellular function which alter cell response to plasma lipoproteins and, at the same time, to define those perturbations of lipoprotein structure which affect their interactions with normal cells. The program, in furtherance of this broad theme, is divided into four main areas: (1) the hepatic synthesis of lipoproteins focused on the apoproteins, (2) the catabolism of lipoprotein-apoproteins, (3) the interaction of lipoproteins with cultured cells, and (4) lipoproteins and membrane structure. These four main areas constitute important aspects of the cellular and molecular biology of lipoproteins.